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Systems Analysis of the Potential Evolution of the Aura Mission

(as of March 20, 2023)

Systems Analysis: Potential Evolution of the Aura Mission

The Aura satellite and its instruments are in good/excellent health, having aged well. This status is expected to continue to the end of the mission. Insufficient power generation by the solar array is conservatively predicted to be the life-limiting factor for the Aura satellite and instruments by mid-2025. However, recent calculations indicate that this date may change (i.e., move into 2026), depending on how the factors (e.g., solar array degradation rate and intensity of the current solar cycle) that affect the lifetime evolve. Therefore, the lifetime projection will need to be updated (e.g., in 2024).

Aura Power Generation

Insufficient power generation (by the solar array) is predicted to be the life-limiting factor for the Aura Mission. The intersection of the two lines represents when Aura will have insufficient power for continued operations; the small excursions in late 2025 and early 2026 won’t likely be a problem as these estimates are generally conservative. The increase in the number of “strings” on the solar array required in mid-2026 is driven by an increase in the solar beta angle, which determines the amount of power generated. The cause of the increase in the solar beta angle is discussed in the following slides.

Aura Number of Strings Required Projection

Spacecraft Fuel

Since launch in 2004, the polar sun synchronous orbit of the spacecraft has been stable and repeatable through periodic spacecraft maneuvers (i.e., inclination adjust, IAM, and drag make-up, DMU, maneuvers), which require fuel to maintain Aura’s position in the A-Train constellation of satellites. The final IAMs will be done in April 2023 to save remaining fuel. Consequently, the spacecraft will slowly begin to drift over time (next slide). The final DMUs were performed in January 2023, so the spacecraft will slowly begin losing altitude, but only a few kilometers by the end of the mission. Aura will have sufficient fuel remaining to do risk mitigation maneuvers (RMMs) for mission safety and the final Perigee Lowering Maneuvers (PLMs) at mission’s end.

The fuel remaining declines towards the approaching of Aura's A-Train Constellation exit

Aura Orbit Evolution

An indicator of the drift is the mean local time (MLT) crossing of the spacecraft over the equator during the day. The graph shows the possible temporal evolution of this drift, which is <15 min through late-2024 and ~28 min by mid-2025. Overall, this amount of drift is predicted to be minor from the perspective of data quality for all MLS and OMI data products. That is, the MLS and OMI instrument teams will be able to account for this minor drift in the data product retrieval algorithms. Perigee lowering maneuvers are shown as taking place in July 2025, but this date may slip into 2026.

Aura: Mean Local Time at Ascending Node

Aura’s Beta Angle

As mentioned in the previous slide, the MLS and OMI retrieval algorithms can account for potential changes in the solar beta angle so that data product quality will be unaffected. The plot below shows the solar beta angle in late 2025 will violate OMI’s “science upper limit” – the range for which OMI was calibrated.

The OMI solar spectral irradiance (SSI) data product is sensitive to changes in the beta angle.

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